The present invention relates to a clutch valving circuit for an automatic transmission, particularly in a hybrid electric vehicle.
A hybrid electric vehicle may be powered alternatively or simultaneously by an internal combustion engine and an electric motor to maximize fuel economy. The electric motor may be part of an electric machine, referred to herein as a motor-generator, which may replace the conventional starter motor and alternator. To move the vehicle from a stopped position, the motor-generator draws electrical energy from a battery pack to turn the engine crankshaft. As vehicle speed increases, fuel and spark are delivered to initiate engine operation. At a certain vehicle speed range, the motor-generator may operate as a generator driven by the engine crankshaft to recharge the battery pack and to supply electrical power to auxiliary vehicle devices such as fans, radios, etc.
When the vehicle is coasting or braking, fuel flow to the engine may be stopped to improve fuel economy. During fuel-off deceleration downshifts, the motor-generator may operate as a motor to synchronize engine and transmission speeds by increasing engine speed to permit a downshift. As the engine speed decreases to a point where engine compression pulsations would be perceived adversely by the driver, the transmission is shifted into a neutral gear to allow the engine to stall. When the engine crankshaft is no longer spinning, the transmission pump operatively associated with the crankshaft likewise does not spin and therefore does not develop hydraulic pressure. In a conventional first clutch circuit, flow thereto is controlled by a manual valve, operated by driver-input through a shift lever. If there is no apply pressure but the path through the manual valve is still open as the vehicle is still in drive, then the first clutch circuit exhausts therethrough. When the driver attempts to re-accelerate the vehicle, there is no apply pressure to activate the first gear clutch needed for the drive gear.
The need exists for a simple way to modify a transmission clutch circuit, designed to be used solely in conjunction with an internal combustion engine, to now be used with a hybrid power source with minimal hardware modifications. More particularly, in xe2x80x9cdrivexe2x80x9d mode, the transmission clutch circuit must enable the first gear clutch to remain applied even when the engine crankshaft, and thus the transmission pump, are not rotating.
The present invention provides a first clutch valving circuit for an automatic transmission, particularly for use in a hybrid electric vehicle. The circuit operates to maintain the first gear clutch in an engaged state when the transmission is in drive, even when the transmission pump is not pressurizing the circuit. The first gear clutch is exhausted when the driver shifts out of drive.
The first clutch circuit comprises an apply line extending from a manual valve to the first gear clutch, with a check ball disposed in the apply line operable to move out of the apply line upon upstream fluid pressure, and an exhaust line extending from the apply line, downstream of the check ball, to an exhaust valve. When the exhaust valve is open, the clutch pressure is released. The check ball ensures that clutch pressure is maintained even when there is no pressure generated by the transmission pump.
A driver-triggered valve actuating means operates to close the exhaust valve when the driver selects drive with a driver shift lever and to open the exhaust valve when the driver shifts out of drive thereby releasing the clutch. The actuating means may be an electronic means such as an electronic signal from the driver shift lever to a solenoid operating on the exhaust valve. Preferably the actuating means may be a mechanical linkage between the driver shift lever and the exhaust valve.
One such mechanical valve actuating means comprises a rooster comb assembly including a rooster comb shaft rotatably operated on by the driver shift lever and a rooster comb fixedly mounted to one end of the rooster comb shaft for rotation therewith about a shaft axis and having a slotted window defined by a cam-shaped edge. The rooster comb assembly operates in conjunction with a gimbal. The gimbal is rotatable about a gimbal axis perpendicular to the shaft axis and includes a catching rod, extending through the slotted window in the rooster comb. The gimbal also includes a cammed actuating surface in close spatial adjacency with an actuating end of the exhaust valve. When a driver selects drive with the driver shift lever, the rooster comb rotates to a position corresponding to drive, the catching rod of the gimbal extends through the slotted window, and the cammed actuating surface of the gimbal does not displace the exhaust valve. Therefore the exhaust valve is in a closed state. When the driver shifts out of drive, the rooster comb rotates, displacing the slotted window wherein the cam-shaped edge of the window applies a force to the gimbal catching rod, rotating the gimbal such that the cammed actuating surface contacts and opens the exhaust valve to release the clutch.